ABSTRACT—: It has recently been shown that the influenza virus can specifically bind the residue of a nonsialylated sulfated oligosaccharide Gal(6SO3H)β1-4GlcNAcβ (6′SLacNAc). To identify by photoaffinity labeling the virion component that binds 6′SLacNAc, we synthesized a carbohydrate probe containing a I labeled diazocyclopentadien-2-yl carbonyl group as an aglycone. According to the electrophoretic data, the labeled areas corresponded to a large hemagglutinin subunit, a nucleocapsid protein, and neuraminidase (NA). Probing in the presence of an excess of 6′SLacNAcβ-OCH2CH2NHAc glycoside resulted in redistribution of the labeling intensity, with the maximum inhibition being observed for NA. The data obtained indicate that NA is a viral 6′SLacNAc-binding protein.